Spaceborne environmental detection lidar, acquiring vertical profiles of environmental information at both day and night, has become an important remote sensing technology for several countries. After nearly 30 years of development, this technology has obtained a large amount of global surface information and atmospheric oceanic environmental information, which has made a great contribution to the rational utilization of earth resources and dealing with global ecological environment and climate problems. In this paper, the development history of spaceborne environmental detection lidar is summarized. The key technologies including the space-borne lidar simulator, satellite-ground validation, and data processing and application are emphasized. The future development directions of spaceborne environmental detection lidar are discussed. The background knowledge of spaceborne environmental detection lidar and its key technologies are introduced to help researchers understand how spaceborne environmental detection lidar provides key data for earth system detection, so that the data accuracy can be better guaranteed and lidar data can be more applied into earth science studies.

Aerosol has always been an important factor in environmental climate, air quality, and public health. Satellite remote sensing can realize the observation of the earth's large field of view and has become one of the mainstream methods of aerosol detection. In order to understand the development status and trend of spaceborne aerosol passive optical remote sensing instruments, this paper investigates the main technical parameters of spaceborne aerosol optical remote sensing instruments in different countries in history based on multi-spectral, multi-angle, and polarization observations. Firstly, the design parameters of several typical instruments in the world and their specific applications in aerosol parameter inversion are introduced in detail. Then, the advanced remote sensing instruments to be launched are analyzed. Finally, the development direction of spaceborne aerosol passive optical remote sensing instruments in the future is summarized. In addition, the paper points out that the integration of multi-spectral observation, multi-angle observation, medium spatial resolution, large field of view, and high-precision polarization measurement is the development trend of spaceborne aerosol optical remote sensing instruments in the future.

Underwater imaging technology plays an important role in military, marine development and engineering applications. However, clear underwater images can hardly be obtained by traditional imaging methods due to the influence of absorption, scattering, turbulence, and complex interaction between light and matter in the propagation process. In recent years, underwater ghost imaging has gradually become a research hotspot. It uses a bucket detector without spatial resolution to obtain the spatial distribution of targets by the correlation algorithm. Compared with traditional array imaging, ghost imaging has the characteristics of high sensitivity, anti-interference and wide working wavelength, and it has prominent advantages in low light, special bands and increasing the detection distance of the imaging system. This paper reviews the research progress of underwater ghost imaging in recent years, focuses on its development process, optical path structure and key technologies, analyzes the factors affecting the quality of underwater ghost imaging and the improvement methods, and predicts the application directions of underwater ghost imaging.

In recent years, with the advancement of metamaterials, mid-infrared metasurfaces have achieved fast development and their various applications have also been explored. Here, various types of mid-infrared absorbing metasurfaces with their mechanisms are introduced. Then, some application methods and advantages of the absorbing metasurfaces in thermal radiation, thermal camouflage, and detectors are summarized. At last, the existing challenges are summarized and further applications are prospected.

Halide perovskite and perovskite-like materials have emerged as very promising optoelectronic materials in the field of X-ray detection, including both direct methods and indirect methods. Due to their remarkable performances, such as strong X-ray stopping capacity and cost-effective manufacturing, the research advances of perovskite X-ray detection have achieved significant progress and attracted lots of attention worldwide. Meanwhile, perovskite based X-ray imaging systems have been successfully demonstrated as well. In this review, we will firstly introduce some fundamental principles of X-ray detection and imaging, summarize the advances of X-ray detection and imaging based on novel metal halide semiconductors and scintillators, and finally put forward some issues and outlooks.

Optical micro/nanofibers are one-dimensional free-standing waveguiding structures with diameters close to or smaller than the vacuum wavelength of the guided light. Fabricated by physically drawing glass fiber at high temperature, these fibers show excellent surface smoothness and diameter uniformity, high mechanical strength, tight optical confinement, strong evanescent field, evident surface field enhancement, and large wavelength/diameter-dependent waveguide dispersion, especially much lower waveguiding loss than all other micro/nanowaveguides with similar geometries. These merits offer them great potentials in applications ranging from near-field optical coupling, optical sensing, atom optics, nonlinear optics, laser technology,and optomechanics. In this review, starting from the basic waveguiding properties of optical micro/nanofibers, we introduce our recent progress in high-precision fiber fabrication and micro/nanofiber-based near-field coupling, optical sensors,and nonlinear optical devices. At same time, we also mention relative works from other groups. Finally, we conclude this article with a brief outlook.

In this paper, the research progress of photonic crystal fiber optic gyroscope (PCFOG) is introduced based on the work carried out by Beihang University. In terms of optical fiber development, photonic crystal fibers (PCFs) with a diameter of Φ110 μm for 1550 nm high precision fiber optic gyroscope (FOG) and superfine solid core polarization-maintaining PCFs with diameter of Φ100 μm for 850 nm miniaturized FOG have been designed and fabricated. The batch preparation technology of km-level hollow core photonic crystal fibers has been broken through. In terms of gyroscope applications, the accuracy of the interferometric fiber optic gyroscope with solid-core photonic crystal fibers has reached 0.001 (°)/h, and the application in spacecraft has realized for the first time worldwide to our knowledge. The hollow-core interferometric PCFOG prototype with the prototype accuracy of 0.4 (°)/h has been fulfilled. Meanwhile, the application of hollow-core PCF in resonant fiber optic gyroscope has also been investigated.

The network data traffic has exhibited an explosive growth trend in the last few years. As the foundation of the global broadband network, optical fiber communication systems have carried more than 90% of the data traffic and developed towards multi-dimension, ultra-large capacity, and ultra-long distance. In this paper, we build an ultra-high capacity-distance product single-mode fiber transmission experimental system to simulate transoceanic transmission. In the transmitter, according to the optical signal-to-noise-ratio of the transmission link, different information entropies are used to generate polarization multiplexing probability shaping 16-order quadrature amplitude modulation signals with different transmission rates. The fiber transmission link is composed of the ultra-low loss large-effective-area fiber and the ultra-wideband low-noise C-band erbium-doped optical fiber amplifier. The experimental system uses 129 wavelength channels (the wavelength range is 1529.8 nm to 1568.2 nm) and realizes the transmission capacity of 28.09 Tbit/s and the transmission distance of 12000 km. Therefore, a capacity-distance product of 337 Pbit·s-1·km is achieved.

Since the 1970s, the interferometric fiber-optic gyroscope (IFOG) technology based on the Sagnac effect, which boasts unique advantages, has developed rapidly with the increasing application and maturity of optical devices such as optical fibers, light sources, and phase modulators in optical communication. Over the past 40 years, this technology has moved from the laboratory to various practical fields such as land, sea, air, and space. This paper reviews the recent development of the IFOG technology. Firstly, the exploration process of this technology from the birth of the Sagnac effect to its practical applications is introduced. Secondly, the classical minimum reciprocity configuration of IFOGs and the signal processing scheme are described. Then, the research status of this technology in high precision, miniaturization, and application environment adaptability is summarized. Finally, the development and application trends of this technology are analyzed.

Spectral imaging can simultaneously obtain two-dimensional spatial and one-dimensional spectral information of the object, which plays an important role in scientific detection and research. Conventional spectral imaging systems have problems such as complex optical systems, precision moving devices, and long exposure times, which greatly limit their application in many scenarios. In this work, a snapshot hyperspectral imaging system based on diffractive rotation is introduced, which can obtain the hyperspectral information of the target through single shot and image reconstruction. We also propose a series of system optimization methods to improve the performance and practicality of the system. The back focal length of the optical system is shortened by using the hybrid diffractive-refractive system, and the long-distance target can be detected by introducing a telephoto optical system in the front. Experimental results show that the optimization methods proposed in this work can effectively increase the exposure ability and improve the quality of the reconstructed image.

Positron Emission Tomography (PET) is a nuclear medical imaging technique for functional in vivo imaging. In order to image in vivo physiological activities from different aspects, dual-tracer PET approach is further proposed. By injecting two different tracers simultaneously, the radioactive concentration distribution of two tracers can be acquired within one single scan. Nowadays, dual-tracer PET has been applied on the diagnosis and treatments of tumors and neurological diseases. Due to the indistinguishable photon energies emitted from two tracers, dual-tracer PET reconstruction becomes challengeable. PET imaging mechanism, tracers and dual-tracer PET reconstruction are introduced, and the pros and cons of those reconstruction methods are discussed as well. In the end, the possible applications of dual-tracer PET imaging on multi-parameter and multi-mode imaging are prospected.

As a high-precision non-contact measurement method, the deflectometric measurement technology can achieve the testing without damaging the surface of the measured components, and it has a high spatial resolution and a large dynamic range. The deflectometric measurement system is simple in configuration, and it has a good application prospect in the field of complex optical freeform surface measurement, which requires high precision, high efficiency, and high versatility. This paper firstly reviews the complex surface measurement methods in recent years and analyzes the corresponding measuring characteristics. Then, it focuses on the introduction to the computer-aided deflectometric measurement technology and the key performance parameters in the computer-aided deflectometric measurement system. After that, the research progress in the key techniques in the deflectometric measurement is discussed, including the measurement model construction, geometrical error calibration, phase acquisition, and surface reconstruction. Finally, the typical applications of computer-aided deflectometric measurement technology are summarized.

With the explosive development of aerospace technology and the rapid advancement in space power, space activities have become increasingly frequent. As a result, a huge amount of space debris is generated, which seriously threatens the safety of on-orbit spacecraft and astronauts. Considering the potential danger brought by space debris, it is particularly important to quickly observe the state of space debris and obtain characteristic information such as size, shape, and motion states. This paper summarizes the existing space-based space-debris observation systems and their technical means and puts forward some development suggestions to explore the development trends of space-based space-debris observation means and provide a reference for the construction of future space-based space-debris observation systems.

This paper introduces a picometer measurement technology based on picometer comb. In the experiment, picometer comb is made by using twice exposed holography with a difference of 200 pm between the periods of two interference fields. When picometer comb is illuminated with a laser beam, it will produce interference fringes along the propagation. Since the period of the interference fringe is in reverse relation with the picometer difference of picometer comb, it implies a new principle of measuring the picometer displacement or variation. Based on the picometer measurement technique proposed in this paper, a new series of picometer-level optical elements, technique, and apparatus will be established in the near future.

A high power solid laser facility used for inertial confinement fusion (ICF) demands over ten thousands of large aperture optics. Extremely precise machining accuracy specified over a continuous range of spatial frequencies (μm-1 level to m-1 level) as well as high resistance to laser damage is the fundamental requirement for high power laser optics. Advanced and deterministic optical manufacturing technologies are the basis to realize mass manufacturing of the large aperture laser optics. In this review, recent progresses in the ultra-precision manufacturing technologies and equipment for high power laser optics are summarized. Advances of ultra-precision grinding, rapid conformal polishing, deterministic polishing, ultra-precision fly-cutting, and low-density defect manufacturing technologies are emphasized. Besides, future developments of fabrication of high power laser optics are analyzed.

Due to its prominent advantages such as complementary metal oxide semiconductor (CMOS) compatibility and high integration, silicon photonics technology is recognized as the most promising new generation of mainstream photonic integration technologies and has thus attracted great attention worldwide. On the one hand, great progress has been made in the research field of passive/active silicon photonic devices and integrated circuits in recent years. Silicon photonics technology has ushered in a broader space for application owing to the rapid development of emerging fields, such as optical communication, optical interconnection, optical sensing, optical measurement, and optical computing. On the other hand, silicon photonic devices and circuits are also exposed to various challenges as they are desired to achieve better performance, higher density, and larger scale. This paper focuses on high-performance passive silicon photonic waveguide devices for wavelength division multiplexing, polarization multiplexing, mode multiplexing as well as hybrid multiplexing, particularly on their performance breakthrough and function expansion. Finally, the prospects of silicon photonic waveguide devices are discussed and presented.

The ultrashort and ultra-intense pulsed laser is an important means of producing comprehensive extreme physical conditions with ultra-high energy density, ultra-strong electromagnetic fields, and ultra-fast time scale in the laboratory. The development status of ultrashort and ultra-intense pulsed lasers, the development trend of ultrashort and ultra-intense pulsed lasers, and the diverse needs of scientific experimental research on high-energy-density physics are analyzed. On this basis, the scheme of the XingGuang-extreme laser facility (XG-ELF) with multiple loading-diagnostic physical experimental functions is proposed, which is composed of three kinds of pulsed lasers with different pulse widths (i.e., two femtosecond lasers of 10 PW, a femtosecond laser of 1 PW@1 Hz, a picosecond laser of 1 kJ, and a nanosecond laser of 10 kJ) that collaboratively output to four physical experiment stations. Moreover, the assumptions and main design results of the physical experiments on XG-ELF are introduced. The completed XG-ELF will provide an advanced experimental platform for research on the frontiers and basic fields of high-energy-density physics in China.

The applications of ocean exploration lidars and underwater wireless laser communications put forward special requirements for the wavelength, repetition rate, and peak power of the laser source. The nanosecond pulsed blue-green laser with high peak power, especially blue laser with smaller attenuation coefficient in ocean water, is widely required for active oceanic remote sensing and high-speed information transmission. In this paper, the development status of blue pulsed lasers is reviewed, and the recent research on blue pulsed lasers emitting at the Fraunhofer line of 486.1 nm is introduced in detail from the perspective of two application scenarios, i.e., one with high repetition rate and multiple wavelengths and the other with high energy and high peak power.

As the demand for network bandwidth is growing explosively, the deployment of the wavelength division multiplexing technology is extending from the backbone network to the metropolitan area network and the access networks. Low-cost tunable semiconductor lasers, which are the core components of wavelength division networks, are attracting increasing attention. This paper reviews the development of semiconductor tunable lasers, describes the working principles and performance of various tunable lasers, and analyzes the advantages and disadvantages of typical commercial tunable optical modules. The research and industrial application progress of low-cost tunable V-cavity lasers are mainly introduced.

Fused silica optics are highly susceptible to rear-surface damage under irradiation by ultraviolet pulsed laser with high energy density,which seriously affects the reliability of high-power ultraviolet pulsed laser facilities. Comprehensively analyzing the related research progress in China and abroad, this paper systematically expounds the damage characteristics of the surface of fused silica optics under high-energy ultraviolet pulsed laser irradiation, including typical initial damage and characteristics of damage growth behaviors. Subsequently, it outlines the types and distribution characteristics of the defects on the surface of fused silica optics, and the intrinsic mechanism of damage induced by ultraviolet pulsed laser. Then, commonly used surface processing methods and defect control technologies for fused silica are summarized. Finally, an overview of the research progress on new non-destructive detection technologies for defects on the surface of fused silica and damage-resistant performance testing technologies is presented.

Laser direct writing (LDW) technique has been widely used in various scientific fields because of its flexible 3D micro/nano-structure processing and manufacturing capability. Due to the diffraction limit, it is challenge to get sub 100 nm or sub 50 nm resolution and realize high throughput 3D nano-manufacturing, which is critical important for the integrated circuit industrial applications in the post-Moore law period. From the perspective of optical imaging, it is concerning with superresolution imaging with large field of view, i.e., maximum throughput spatial passband product. LDW technique focuses on writing with high throughput and high resolution. This paper will expound on the development of the LDW technique and introduce our research group's progress in the high throughput LDW technique.

Wide band gap semiconductors have the characteristics of unique electronic structure, rich micro/nano structure, low temperature controllable preparation, flexible transparency, good chemical stability, abundant and inexpensive, etc., which make it become a new important basic material of information technology and environmental technology. Taking zinc oxide and perovskite as two wide band gap semiconductor materials, the preparation principle and method, photoelectric properties, and applications in the fields of ultraviolet light sources, transparent conductive thin films, and light-emitting diodes of the two materials are summarized. Finally, the prospect of its development is given.

In recent years, methods for large-depth optical imaging of biological tissues, such as optical coherence tomography, multi-photon imaging, and adaptive optics, have been developed continuously. This paper outlines a series of important advances in large-depth quantitative optical imaging of biological tissues achieved by the College of Optical Science and Engineering of Zhejiang University in recent years, including structural and functional optical coherence tomography, large-depth cerebral vascular imaging based on three-photon fluorescence microscopy, and new wavefront correction methods for distortion errors. It also summarizes the ways of quantitatively characterizing the optical images obtained by these methods to acquire physiological and pathological information about biological tissues.

Structured light field usually has unique optical characteristics in spatial distribution, and is widely used in the fields of microscopy, imaging, communication, and measurement. There are many kinds of structured light devices with different materials and modulation mechanisms. There are great differences in the performance indicators such as modulation speed, modulation depth, and spatial resolution. This paper introduces the working principle and performance characteristics of the main structured light devices (liquid crystal spatial light modulator, digital micromirror device, silicon-based optical phased array, LED array, etc.), analyzes their respective application ranges, and summarizes the typical applications of structured light technology in the fields of display projection, microscopic imaging, ghost imaging, three-dimensional imaging, lidar, etc. This paper systematically shows the latest research progress and cutting-edge technology applications of a variety of structured light devices, which will provide reference for researchers in related fields.

A variable curvature mirror is a kind of active optical element. By changing its curvature radius, the corresponding wave-front could be dynamically controlled. First of all, the current situation and development trend of variable curvature mirrors are summarized systematically. After that, the physical model of deformation of variable curvature mirrors with variable thickness is established and the capability of this kind of variable curvature mirror in generating large saggitus and maintaining good surface figure accuracy is proven through numerical simulation and experiments. Finally, the application of variable curvature mirrors with variable thickness in space optical cameras is explored from three aspects. In the first place, in order to satisfy the requirement for the super large saggitus variation required by realizing large magnification ratio zoom imaging, a finite element alternating (FEA) based optimization procedure by incorporating high-order spherical deformation is designed, and the mirror with the saggitus variation approaching 1 mm is obtained. In the second place, aiming at the requirements of focusing accuracy and speed in space camera imaging, a high-precision large dynamic focusing method based on sub-mirror variable curvature mirrors is proposed. In the third place, a coding imaging method using a variable curvature secondary mirror to scan quickly along the optical axis during integration time is proposed.

Ultra-wideband arrays have been a trend of development of radar, communication, and electronic information systems. Microwave photonics (MWP), combining the advantages of both microwave and photonic technologies, will pave the way for the development of electronic information systems with novel mechanism. In this paper, the domestic and foreign research progresses of MWP are reviewed. A signal processing architecture based on MWP technologies and adapted to multiple scenarios is discussed. The research progresses in theories, experiments, and applications of typical MWP technologies, such as high quality signal generation, large dynamic signal transmission, phase stabilization of distributed signals, optical beamforming, and optical channelization, are described. In the end, the development trends of microwave photonics are expected.

Because of its intrinsic topological charges (TCs), a vortex beam offers a Hilbert space with a higher dimension when it is utilized as a carrier of space optical communication. As a result, optical communication based on vortex beams enjoys significantly improved channel capacity and security. At the channel receiver in optical communication, TCs need to be identified accurately and rapidly to decode the transmitted information. In this paper, the dimension of polarization state is introduced into the process of TC identification, and the influence of polarization state on TC identification is studied from the perspectives of numerical simulation and experimental verification. Interference images of a signal beam and a reference beam with different polarization states in a Mach-Zehnder interferometer are analyzed. The results show that the Gaussian beam (reference beam) with the circular polarization state is the most favorable choice for identifying the TCs of the vortex beam (signal beam) with the same polarization state, and these signal beam and reference beam also appear to be least sensitive to the angle of the interference optical path during TC identification. The theoretical simulation is in good agreement with the experimental data, which indicates that the proposed polarization interference-based TC identification scheme provides a reference for future high-speed and high-capacity optical communication based on vortex beams over distances in the order of magnitude of several kilometers.

Forest biomass detection is the assessment basis of the carbon sequestration capacity of forest ecosystems, and it is of great significance for research on the carbon cycle of terrestrial ecosystems. The development of remote sensing technology provides an effective way to obtain forest biomass quickly and accurately. The paper first introduces the development of forest biomass estimation by remote sensing satellites in China and abroad, discusses the applicability of optical remote sensing, lidar and microwave radar data in forest biomass estimation, and summarizes the existing problems. Then, the requirements and tasks of the new generation of remote sensing satellite for forest biomass estimation in China are put forward. Considering the technical difficulties in high-precision and quantitative remote sensing measurement of forest biomass, the task analysis process and the load alloccation scheme are given. The scheme can realize the multi-load observation on the same platform and three-dimensional atmospheric aerosol detection. Finally, the future development of forest biomass remote estimation by sensing satellites is predicted.

The spectral imager can accurately detect the composition and temperature of the lunar surface and their variable characteristics, becoming a key scientific payload in the new era of lunar scientific exploration missions, which provides scientific data for further cognition of the origin and evolutionary history, resource distribution, and environmental characteristics of the lunar. The existing spectral imaging data of lunar orbit exploration provide scientific reference for human cognition of lunar surface material composition, resource distribution, and evolutionary history, but there are problems of low spatial resolution and few infrared spectral bands for realizing precise exploration of lunar resources and environment development and application. The paper firstly outlines the typical spectral imaging payloads and research hotspots in lunar exploration missions at home and abroad. Secondly, the specific technical challenges faced are discussed specifically for the precise detection needs of lunar spectra. Then, specific solutions and technical approaches are proposed on how to break through the existing technical challenges and obtain higher resolution, more sensitive, and more reliable spectral scientific data. Finally, the development trend, challenges, and applications of spectral imaging for lunar orbit exploration are summarized and prospected.

Ultrafast laser has features of ultrafast speed, ultra-high intensity, and ultra-wide spectrum. Focused ultrafast laser can instantaneously generate extremely high temperature and pressure within transparent materials. Under such local extreme conditions, many new changes in the internal structures of the materials take place. Taking all-inorganic halide perovskite nanocrystals (PNCs) as an example, the basic principle of ultrafast laser-induced nucleation and nanocrystal precipitation in glass is expounded. Researches conducted in recent years on the precipitation of all-inorganic PNCs in glass by ultrafast laser are summarized, and the applications of this technology in the fields of optical storage and color display are analyzed.

In recent years, the emerging metal-halide perovskite materials have shown the great potential of breaking the technological bottleneck of traditional optoelectronic semiconductors as they enjoy many advantages of both inorganic and organic light-emitting materials, such as large-area preparation by the solution method, easy band-gap tunability, high carrier mobility, and high photoluminescence quantum efficiency. Perovskite light-emitting diodes (LEDs) are regarded as the most promising next-generation lighting and display technology to achieve low-cost, high brightness, large area, and flexible devices. This paper mainly introduces the progress made by our group in perovskite LEDs, summarizes the main strategies to improve device performance, and predicts the development directions of perovskite LEDs.